Iraq deployed elite troops to the besieged provincial capital of Ramadi on Thursday in hopes of stemming an Islamic State offensive but the city remained surrounded, with Islamic State forces in control of many, if not most, districts, according to witnesses and government officials.

The Islamic State also claimed that its fighters had entered the strategic oil refinery at Baiji, a huge reversal for the government, which until Thursday had prevented the radicals from gaining a foothold in Iraq’s largest oil-processing center.

The two battles 120 miles apart marked major setbacks for the government in Baghdad just two weeks after it triumphantly captured the city of Tikrit from the Islamic State, and they were a reminder that Iraqi forces still face an uphill climb in wresting much of their country from the group. The troops dispatched to Ramadi on Thursday were the same well-trained Interior Ministry commandos who’d spearheaded the final assault on Tikrit.

What their impact would be on the battle remained to be seen. Residents on Wednesday had described a near-total collapse of Ramadi’s defenses, with huge numbers of security forces abandoning large portions of the city in the face of the Islamic State assault.

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In Washington, Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, tried to downplay the importance of the setback at Ramadi, which he called “not symbolic in any way.”

“It’s not been declared part of the caliphate . . . or central to the future of Iraq. But we want to get it back,” he said. “It won’t be the end of the campaign if it falls.”

“Baiji is a more strategic location,” he said.

An Iraqi Interior Ministry official told local television Thursday that the newly arrived commandos had opened an approximately 10-mile stretch of roadway that links parts of central Ramadi to the eastern district of Sufiya and the town of Sajariyah. Residents described Ramadi as still under siege from the north and east, and said Thursday’s gains were only allowing civilians to flee.

Tens of thousands of civilians remain trapped in the city, many of them from pro-government Sunni Muslim tribes who’d fought alongside the mostly Shiite Muslim security forces to keep the Islamic State out of Ramadi. Residents reported new, apparently unaligned militias taking to the streets to protect neighborhoods and fill the vacuum left by fleeing security forces.

“These are neighborhood youth. They’re not with the government or with Daash,” said one resident, using the Arabic acronym for the Islamic State. “They will end up on the side of whoever wins.” He asked not to be identified out of concern for his safety.

The resident supplied phone-camera video of masked gunmen taking positions in areas clearly identifiable as the Ramadi city center – within several hundred yards of provincial government compounds, which as of nightfall remained in government hands.

Speaking from Baghdad, where he’d fled Wednesday along with at least 10,000 civilians who’d managed to cross about 50 miles of Islamic State-held territory, a member of the Anbar Provincial Council, Athal Fahdawi, told McClatchy that the Islamic State now completely controlled the eastern portion of the city, an area that links Ramadi to mostly Islamic State-held Fallujah and the highway to the nation’s capital, Baghdad.

“Daash dominates the eastern part of the city,” he said. “And Daash is besieging from all sides.”

Fahdawi said the militants had taken control of Ramadi after security forces and tribal fighters fled.

An officer within the Anbar provincial operations center, which is coordinating the fight, confirmed the arrival of the special forces commandos and that they’d established a small corridor for refugees to withdraw into portions of the city that remain under government control. He acknowledged that Islamic State suicide bombers had stymied their efforts to break the siege.

The officer said government-aligned fighters had failed in three separate attacks to dislodge Islamic State militants from Karmah, a strategic town near Fallujah. “Daash continues to besiege Ramadi,” said the official, who spoke only on the condition of anonymity, as he lacked permission to talk to reporters. “Karmah is still surrounded.”

Islamic State inroads into the Baiji refinery would mark a major turning point. The group captured the city last July, but a small contingent of government troops had kept control of the refinery. The government retook the city in November, then quickly lost it again, but the refinery, which used to provide 40 percent of Iraq’s gasoline, remained in government hands.

On Thursday, the Interior Ministry admitted on state television that the militants had breached the oil facility’s defenses, killing the commander in charge of the garrison, and that heavy fighting continued at a huge oil tank storage farm on the outskirts of the refinery.

The Islamic State claimed that videos posted on Twitter showed its fighters in the refinery itself, though there was no confirmation. Dempsey said at a Pentagon news conference that he didn’t believe the refinery was in danger of falling to the Islamic State, and added that U.S. aircraft were conducting airstrikes.

“The refinery is at no risk right now, and we’re focusing a lot of air support,” he said.

In addition to the loss of gasoline production, repairing significant damage to the facility would take years, cost billions of dollars and require foreign engineering expertise that Iraq is unlikely to secure in such a hostile security environment.

Contributing to this report were Jonathan S. Landay in Washington and a McClatchy special correspondent in Baghdad whose identity is being kept secret for security reasons.